J-chain is an acidic 15-kDa polypeptide, which is associated with pentameric IgM and dimeric IgA via disulfide bonds involving the penultimate cysteine residue in the 18-amino acid secretory tail-piece (tp) at the C-terminus of the IgM μ or IgA α heavy chain. The three disulfide bridges are formed between Cys 12 and 100, Cys 71 and 91, and Cys 108 and 133, respectively. See, e.g. Frutiger et al. 1992, Biochemistry 31, 12643-12647. Structural requirements for incorporation of the J-chain into human IgM and IgA and for polymeric immunoglobulin assembly and association with the J-chain are reported by Sorensen et al. 2000, Int. Immunol. 12(1): 19-27 and Yoo et al. 1999, J. Biol. Chem. 274(47):33771-33777, respectively. Recombinant production of soluble J-chain in E coli is reported by Redwan et al. 2006, Human Antibodies 15:95-102.
Methods for making hybrid IgA/IgG and IgM/IgG antibodies are known in the art. Thus, recombinant production of hybrid IgA2/IgG1 antibodies is reported in Chintalacharuvu et al. 2001, Clin Immunol 101(1):21-31. It has been reported that addition of αtp or μtp at the end of IgG γ heavy chain facilitates polymerization and enhances effector function such as complement activation (Smith et al., J Immunol 1995, 154:2226-2236). The IgA/IgG hybrid antibodies possess properties of both IgA and IgG.
Despite the advances made in the design of antibodies, there remains a need for modified antibodies with improved properties, such as improved affinity, specificity and/or avidity.
As the field has progressed, antibody function has been enhanced through creative means of protein engineering, such as to provide higher affinity, longer half-life, and/or better tissue distribution, as well as combination of small and large molecule technologies for increased focus of cell destruction via toxic payload delivery (e.g. antibody-drug conjugates). Another approach to improving antibody function takes advantage of the bivalent binding of the immunoglobulin G (IgG) structure which allows one IgG molecule to bind two antigens. Indeed, in certain applications, there exists good potential for asymmetric antibodies to exert useful functions by simultaneously binding two different target antigens. To address this need, a variety of constructs have been produced to yield a single molecule that can bind two different antigens, allowing for functions never before seen in nature. An example of this bi-specific approach is “blinatumomab” (MT103 or AMG103) which binds the CD3 and CD19 receptors, on T- and B-cells, respectively. This tethering of a cytotoxic T-cell to a cancerous B-cell, allows for effective treatment of B-cell leukemia.
However, there remain significant technical difficulties in construction, expression and production of bispecific antibodies. Although bispecific antibodies are regarded as promising therapeutic agents due to their ability to simultaneously bind two different antigens, their utility is limited due to problems with stability and manufacturing complexity.
Various forms of protein engineering have been used to match heterologous heavy chains, plus appropriate pair-wise matching of heavy and light chains to efficiently yield a bi-specific IgG. In addition, various bispecific antibody formats, including quadromas, chemical heteroconjugates, recombinant constructs using selected heterodimerization domains and recombinant constructs of minimal size consisting of two minimal antigen-binding sites.
However, all of these efforts have been fraught with difficulty.
Thus, despite efforts directed toward the development of engineered, such as bispecific, antibodies, there remains a great need for developing more efficient platforms. This is particularly true in the case of therapeutic antibodies, where the design and production of new, modified, antibodies and antibody-like molecules with multiple specificities can shorten the timeline between discovery and clinical introduction of such therapeutics.